The present invention relates generally to heat exchangers, and more particularly to finned tube heat exchanger coils having sine-wave like plate fins including embossed vortex generating enhancements.
Plate fins utilized in the air conditioning and refrigeration industry are normally manufactured by progressively enhancing a coil of plate fin stock by a shearing operation whereby open enhancements are formed on the surface of the fin stock. After the open enhancements are formed, the fin stock is cut to the desired length. The fins are then collected in the proper orientation and number in preparation for forming a coil. Previously formed hairpin tubes are then inserted through openings within the fins and thereafter expanded to form mechanical and thermal connections between the tubes and fins. The open ends of the hairpin tubes are fluidly connected by way of U-shaped return bends, and subsequently the return bends are soldered or brazed in place.
The plate fins are typically manufactured in a die with forming, punching or shearing pins to form the fin shape, the open surface enhancements on the fin, and the openings through which tubular members are inserted.
It is known that a fundamental contributor to the limiting of local convective heat transfer is the establishment and persistence of thermal boundary layers on the plate fin surfaces of heat exchangers. For this reason, prior art fins are provided with a variety of surface variations or enhancements to disrupt the boundary layer and to improve the transfer of heat energy between the fluid passing through the tubular members and the fluid passing over the plate fin surfaces. These prior art enhanced fins are generally either enhanced flat fins or convoluted fins. Flat fins and convoluted fins are generally enhanced by punching or shearing raised lances, louvers, or ramp and delta wings therein. A raised lance is defined as an elongated portion of fin formed by two parallel slits whereby the material between the parallel slits is raised or displaced from the mid-plane of the fin. A louver is defined as an elongated portion of fin formed by one or two parallel slits whereby the material adjacent to a singular slit, or between parallel slits, is rotated about the mid-plane of the fin to a prescribed angle. A ramp or delta wing is defined as a portion of a fin having one side length connected to the fin in a direction generally perpendicular to the direction of fluid flow over the wing while the remaining sides are slit and raised from the surface of the fin. Typical of the previous plate fin heat exchangers utilizing enhancements are U.S. Pat. Nos. 4,860,822 and 4,787,442 assigned to the assignee herein. These lances and wings promote thinning of the hydrodynamic boundary layer and serve to generate secondary flows which increase the heat transfer coefficient. However, generally large numbers of lances and louvers and wings are added to a surface to improve the heat transfer, but these enhancements are always accompanied by an increase in pressure drop through the coil.
Further, such lanced, louvered, and raised winged plate fins may be difficult and costly to manufacture, due to the complex manufacturing problems associated with numerous, small punching stations which are necessary to shear the fin stock to make the enhancements. Still further, the shearing operation results in waste material in the form of scrap fragments which can render the forming die inoperable.
Thus, there is a clear need for a sine-wave like plate fin having an embossed enhanced surface which reduces waste material while improving the heat energy dissipation and increasing the reliability of the forming dies.